The automotive industry, inter alia, is moving toward the use of more and more lightweight metals in order to reduce vehicle weight, improve fuel economy, and improve heat transfer in certain components (e.g., brake drums, engines, etc.).
Brake drums were originally constructed 100% of iron or steel for strength, wear and friction reasons. Subsequently, composite brake drums were used wherein a cast iron or steel liner provided the friction surface and was backed up with an aluminum backing cast thereabout for reducing the weight and improving the heat dissipation of the brake drum. Similarly, some internal combustion (IC) engines have used iron/steel cylinder liners insert molded into cast aluminum blocks. The aluminum reduces the vehicle weight and improves engine cooling.
The production of such composite castings with effective bonding between the insert (e.g., brake or engine liners) and the aluminum cast thereabout has been a continuing problem for many years. Mechanical bonding techniques have been used, but due to the differences in thermal expansion between the insert and the cast metal have encountered some difficulties. Hence in the case of Fe liners cast into aluminum, the aluminum tends to expand away, and separate from, the iron insert resulting in poor and often nonuniform heat transfer. The use of low melting metal coatings (e.g., zinc and its alloys) on the insert prior to casting the metal thereagainst has achieved some success, but even this technique is not free from problems.
Accordingly, it is the principal object of the present invention to simply produce a unique permanent, metallurgical bond between a solid metal or ceramic insert and metal cast thereagainst via an intermediate intermetallic layer formed in situ during casting, the constituents of which diffuse into both the insert and the cast metal to produce a bond which resists separation of the cast metal from the insert even at elevated temperatures typically achieved in brake drums and IC engines. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.